This invention relates generally to semiconductor laser devices and more particularly to devices which operate at wavelengths of 700-850 nanometers with relatively low threshold current values for outputs having a relatively high power.
Currently semiconductor laser diodes are utilized for a variety of applications. Semiconductor diode lasers comprised of GaAs/AlGaAs materials are commonly utilized due to the relative maturity of the growth and processing technology of these materials. GaAs/AlGaAs semiconductor diode lasers are generally utilized in applications requiring wavelengths from approximately 750 nm to 1 .mu.m. The use of such GaAs/AlGaAs diode lasers having wavelengths less than approximately 750 nm has been accomplished, however, the performance of such diode lasers has proven to be rather poor in terms of threshold current density, characteristic temperature and resultant power output. For example, threshold current densities of greater than 4000 A/cm.sup.2 are required for such diode laser systems to operate at 695 nm. This deterioration in performance by GaAs/AlGaAs diode lasers with a decrease in resultant wavelength is generally due to the reduction of barrier heights within the device which in turn decreases the carrier confinement so as to require higher threshold current levels and lower efficiency of the device.
For wavelengths shorter than those for which GaAs/AlGaAs diode lasers can efficiently provide, diode lasers constructed from GaInP/AlGaInP materials grown upon GaAs substrates have typically been utilized. The wavelength of the light output from such diode laser systems, typically varies from less than 630 nm to approximately 700 nm. While there have been recent advances in the performance of GaInP/AlGaInP diode lasers in the shorter wavelength bands, there has been little utilization of GaInP or AlGaInP materials in diode lasers operating at wavelengths much greater than 700 nm.
Previously, semiconductor laser diodes operating within the band of wavelengths between those efficiently produced by the two materials systems previously discussed have been constructed of GaAs/AlGaAs materials due to the relative maturity of the growth and processing technology of these materials even though the performance of such diodes was relatively inefficient in terms of threshold current density, characteristic temperature and power output. Therefore, it would be desirable for a semiconductor laser diode to be constructed to operate with outputs of 700-750 nm while requiring a low threshold current density and having a high characteristic temperature, high internal efficiency, high reliability and a large output power. In addition it would be desirable if such diodes, suitably modified, might also operate suitably in the 750-850 nm band.